As is well known in the prior art, catalyst systems comprising a Group 4 transition metal cyclopentadienyl compound, hereinafter frequently referred to as a metallocene or metallocene catalyst component, and an alumoxane offer several distinct advantages when compared to the more conventional Ziegler-type catalyst systems. For example, the cyclopentadienyl-transition metal/alumoxane catalyst systems, particularly those wherein the cyclopentadienyl compound contains at least one halogen atom, have demonstrated extremely high activity in the polymerization of alpha-olefins, particularly ethylene. Moreover, these catalyst systems produce relatively high yields of polymer product having a relatively narrow molecular weight distribution.
For many applications it is of primary importance for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, generally provides a polymer with high strength properties. Traditional Ziegler-Natta catalyst systems--a transition metal compound cocatalyzed by an aluminum alkyl--are in general capable of producing polyolefins having a high molecular weight but a relatively broader molecular weight distribution.
International Publication No. WO 87/03887 described the use of a composition comprising a transition metal coordinated to at least one cyclopentadienyl and at least one heteroatom ligand as a metallocene type component for use in a metallocene/alumoxane catalyst system for alpha-olefin polymerization. The composition is broadly defined as a transition metal, preferably of Group 4 of the Periodic Table which is coordinated with at least one cyclopentadienyl ligand and one to three heteroatom ligands, the balance of the coordination requirement being satisfied with cyclopentadienyl or hydrocarbyl ligands. The metallocene/alumoxane catalyst system described is illustrated solely with reference to transition metal compounds which are bis(cyclopentadienyl) Group 4 transition metal compounds.
U.S. Pat. No. 5,087,677 discloses polymers of polycyclic olefins, optionally with alpha-olefin and/or monocyclic olefins, prepared with a stereorigid, chiral bridged bis(cyclopentadienyl) transition metal catalyst and alumoxane cocatalyst, which have a relatively high polydispersity value (MWD) between 2.9 and 6.0.
European Patent Application 283,164 discloses copolymers of C.sub.3 to C.sub.20 alpha-olefin and cycloolefin prepared with an alkylene bis(indenyl) zirconium compound and an alumoxane. However, no ethylene or propylene copolymers having both a weight average molecular weight above about 24,000 daltons and a molecular weight distribution less than 2 were reported.
European Patent Application 501,370 discloses polycyclic olefin homopolymers and copolymers with monocycloolefins and/or acyclic alpha-olefins, prepared with a stereorigid, chiral bridged transition metal catalyst and alumoxane cocatalyst, reported to have a molecular weight distribution M.sub.w /M.sub.n less than 2. However, none of the examples show a copolymer having both M.sub.w /M.sub.n less than 2 and an M.sub.w greater than 50,000.
Commonly assigned U.S. Ser. No. 07/133,480, filed Dec. 22, 1987, now abandoned by Turner and Hlatky, discloses olefin polymerization with a bis(cyclopentadienyl) metal compound and a bulky, labile Lewis-acid anion activator such as tetra(perfluorophenyl) borate in liquid olefins which may act as monomers or comonomers including cyclopentene. EPA 277,004, published Mar. 8, 1988, corresponds thereto and is hereby incorporated herein by reference. Similarly, copending application U.S. Ser. No. 07/770,449, filed Oct. 3, 1991, now U.S. Pat. No. 5,194,903 by Canich et al.; which is a continuation-in-part of U.S. Ser. No. 581,841, Sep. 13, 1990; which in turn is a continuation-in-part of U.S. Ser. No. 533,245, Jun. 4, 1990; which is in turn a continuation-in-part of U.S. Ser. No. 406,945, Sep. 13, 1989 now abandoned; discloses polymerizing ethylene in combination with other monomers such as norbornene using a monocyclopentadienyl metal compound and an alumoxane.
Kaminsky et al., Makromol. Chem., volume 190, pp. 515-526 (1989), discloses polymerization of cyclopentene, cycloheptene and cyclooctene with ethylene using chiral catalyst ethylene(bisindenyl) zirconium dichloride/methylaluminoxane to form isotactic copolymers. The ethylene-cyclopentene copolymers are reported to have molecular weights below 24,000 and MWD between 3 and 4.5.